Field of the Invention
The invention relates to copper-containing metal pigments with at least one enveloping metal oxide layer and at least one enveloping plastic layer, as well as a method for the production thereof. The invention furthermore relates to a coating agent, as well as a coated object.
Description of Related Art
Copper-containing metal pigments, in particular metallic effect pigments, such as copper pigments or brass pigments, which are also called gold bronze pigments, are often used in the graphics industry, for example in printer inks.
Copper-containing metal pigments are problematic to use because of their copper content. Copper-containing pigments, for example copper-containing metallic effect pigments, readily release Cu(I) ions to the surroundings, for example a varnish or a paint. The Cu(I) ions readily change into Cu(II) under the influence of moisture. The change in the oxidation state from Cu(I) to Cu(II) is necessarily accompanied by a reduction of components of the surroundings, for example of binder components of a varnish or a paint.
In addition, in particular Cu(II) ions form colored complexes which can have a disruptive effect on the hue of the corresponding application. For example, Cu(II) ions form intensely blue copper complexes under alkaline conditions, in particular in the presence of amines.
Above all, however, the Cu(II) ions, and in the case of gold bronze pigments also of Zn(II) ions, can bring about a gelling of the binder, which makes the corresponding application unusable.
For this reason, for example copper or gold bronze pigments which are coated with SiO2 according to IDE 102 38 090 A1 cannot be reliably used in nail polishes.
The above-named effects are associated specifically with copper-containing metal pigments, and therefore have no counterpart in other metal pigments, for example in metal pigments consisting of aluminum, iron, tin, etc.
According to the teaching of WO 2009/149834 A2, copper-containing metallic effect pigments as well as coating agents with copper-containing metallic effect pigments are provided in which the above-named copper-specific problems are solved in that a cellulose derivative, selected from the group consisting of alkyl cellulose, hydroxyalkyl cellulose, alkyl(hydroxyalkyl) cellulose and mixtures thereof, is present as a further component.
These special cellulose derivatives can theoretically be added to liquid coating agents such as printer inks, varnishes or paints. However, for example incompatibilities often prevent the use of such cellulose derivatives.
WO 2007/017195 A2 discloses in general metallic effect pigments with a coating. The coating is characterized in that it comprises a mixed inorganic/organic layer. The mixed layer contains an inorganic network and at least one organic component, wherein the organic component is an organic oligomer and/or polymer which is at least partially covalently bonded to the inorganic network via one or more organic network formers.
It has been shown that the production of mixed inorganic/organic layers is expensive in terms of process technology.
Metallic effect pigments with a coating are also known in general from WO 2005/063897 A2. These metallic effect pigments are coated with oligomeric and/or polymeric binders that can be chemically cross-linked and/or can be cross-linked under the action of heat, IR radiation, UV radiation and/or electron beams. This still chemically reactive binder coating allows a reaction with the binder of a varnish or a printer ink after application of the metal pigment. A pre-coating with SiO2 can be arranged under the binder coating.
It has been shown that, in the case of copper-containing metal pigments with the coating known from WO 2005/063897 with a not yet cross-linked binder coating, the release of copper ions to the surroundings is not reliably prevented. In addition, relatively large quantities of binder have to be used for the coating, which leads e.g. to a reduced covering capacity.
DE 198 20 112 A1 discloses effect pigments coated with reactive orientation additives. The subject of this application essentially consists of aluminum effect pigments which can be coated with a coating of metal oxides or polymers. Orientation additives which enable a covalent bonding to the binder of a paint or a varnish are then arranged on this coating.
Finally, metallic effect pigments coated with synthetic resin, in particular aluminum effect pigments, are known from DE 40 30 727 A1.
A double coating of SiO2 and a synthetic resin of metallic effect pigments is known from US 2009/0117281 A1. This coating makes it possible to use the metal pigments in aqueous formulations and brings about an improved chemicals stability and water resistance of the films to which it has been applied. US 2009/0117281 A1 is clearly aimed at the use of aluminum effect pigments.
Metallic effect pigments with improved chemicals stability are also described in WO 2008/095697 A1.
With the exception of WO 2009/149834 A2 and WO 2008/095697 A1, the above-listed state of the art relates fundamentally to the coating of aluminum effect pigments, in order to provide corrosion-stable aluminum effect pigments.
Apart from WO 2009/149834 A2, none of the above-named documents from the state of the art addresses the problem that copper-containing pigments release copper ions, which can then lead to undesired effects, to the surroundings.